Functional Group Interconversion Reactions

Elimination reactions to reveal masked dendralenes featured prominently in early attempts to synthesize cross-conjugated compounds [1]. Cheletropic extrusion of sulfur dioxide was used to convert lower dendralenes to [5], [6], and [8] dendralene [10], and to make substituted chiral [4] dendralenes [12]. 

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Functional group interconversion reactions (many name reactions, all generic reactions)... 

FGI Functional Group Interconversion The operation of writing one functional group for another so that disconnection becomes possible. Again the reverse of a chemical reaction. Symbol with FGI written over it. 

Have you noticed that the disconnections involving H" are simply redox reactions and do not alter the carbon skeleton of the molecule They are not then reaUy discoimections at all but Functional Group Interconversions or FGI for short. 

Syntheses by Functional Group Interconversions (Condensation Reactions)... 

Section 15.1 Functional group interconversions involving alcohols either as reactants or as products aie the focus of this chapter. Alcohols aie commonplace natural products. Table 15.1 summarizes reactions discussed in earlier sections that can be used to prepare alcohols. 

A sequence of straightforward functional group interconversions leads from 17 back to compound 20 via 18 and 19. In the synthetic direction, a base-induced intramolecular Michael addition reaction could create a new six-membered ring and two stereogenic centers. The transformation of intermediate 20 to 19 would likely be stereoselective substrate structural features inherent in 20 should control the stereochemical course of the intramolecular Michael addition reaction. Retrosynthetic disassembly of 20 by cleavage of the indicated bond provides precursors 21 and 22. In the forward sense, acylation of the nitrogen atom in 22 with the acid chloride 21 could afford amide 20. 

Another interesting biooxygenation reaction with alkenes, recently identified, represents an enzymatic equivalent to an ozonolysis. While only studied on nonchiral molecules, so far, this cleavage of an alkene into two aldehydes under scores the diversity of functional group interconversions possible by enzymatic processes [121,122]. 

Figure 6.13 Functional group interconversions of methyl, primary, and secondary alkyl halides using Sn2 reactions.

Scheme 3)10. Indeed, independent photolysis of 2,4-cyclohexadien-l-ones 12 and 13 afforded the macrolides 15. These reactions likely proceed via a common intermediate, in this case dienylketene 14, which is trapped intramolecularly by the pendant hydroxyl group. Adjustment of the oxidation level and functional group interconversion then led efficiently to the desired macrolide 17. The sulfonyl group was used for two reasons first, to easily transform lactones 15 into dienyl lactones 16 needed for 17, and secondly, to control the regiochemistry of the Wessely oxidation of phenolic precursor needed to produce the photolysis substrates 12 and 13. 

Hydrogen atom transfer implies the transfer of hydrogen atoms from the chain carrier, which is the stereo-determining step in enantioselective hydrogen atom transfer reactions. These reactions are often employed as a functional group interconversion step in the synthesis of many natural products wherein an alkyl iodide or alkyl bromide is converted into an alkane, which, in simple terms, is defined as reduction [ 19,20 ]. Most of these reactions can be classified as diastereoselective in that the selectivity arises from the substrate. Enantioselective H-atom transfer reactions can be performed in two distinct ways (1) by H-atom transfer from an achiral reductant to a radical complexed to a chiral source or alternatively (2) by H-atom transfer from a chiral reductant to a radical. 

Advantageous Electrochemical C,C-Bond Forming Reactions and Functional Group Interconversions I 79... 

The functional group of an organic molecule is its reactive part and, as such, is responsible for the reactions that molecule will undergo. We have now accumulated a fair bit of knowledge about different functional groups and the connections between them. These functional group interconversions are summarised in the diagram on p. 71. 

With your knowledge of organic reactions, functional groups and functional group interconversions, you are now in a position to apply this knowledge in devising a synthetic route from a given reactant to a final product. 

Very often these reactions are traditional and illustrative, but they are not necessarily the best way to manipulate a particular functional group. Many traditional methods have been replaced, in practice, by newer reactions or reagents which offer certain advantages over older methods. In general, these advantages have to do with mild conditions, selectivity, generality, and/or experimental simplicity. Nevertheless all types of functional group interconversions, new or old, are still based fundamentally on the ideas that have been developed earlier in this book. 

The bulk polymeric format, characterised by highly cross-linked monolithic materials, is still widely used for the preparation of enzyme mimic despite some of its evident drawbacks. This polymerisation method is well known and described in detail in the literature and has often be considered the first choice when developing molecular imprinted catalysts for new reactions. The bulk polymer section is presented in three subsections related to the main topics covered hydrolytic reactions, carbon-carbon bond forming reactions and functional groups interconversion. 

In the case of (11), retrosynthetic functional group interconversion into the aldol followed by disconnection of the a, /3-bond gives the dipolar synthon (15), of which the reagent equivalent is the 1,4-dicarbonyl compound, hexane-2,5-dione (i.e. a refro-aldol condensation). The action of base on this diketone effects the forward aldol reaction followed by spontaneous dehydration (see Expt 7.4 for formulation). 

The two target molecules, which illustrate cyclisation reactions involving substituted 1,5-dicarbonyl compounds in the presence of appropriate reagents, are diethyl 2,6-dimethylpyridine-3,5-dicarboxylate (85) and 2,4,6-triphenylpyrylium fluoroborate (86). The latter is of specific interest since it provides a simple example to illustrate a general procedure for the conversion of pyrylium salts into pyridinium derivatives these latter compounds are important reagents for a variety of functional group interconversions (see Sections 5.5.6, p. 574, and 5.15.3, p. 768). 

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